This invention relates in general to a digital audio player, and more particularly to a wireless output input device player for relaying a digitally encoded stream of audio to a mobile, stationary or portable FM receiver.
Heretofore, it has been known to provide a portable CD or MP3 player for wireless playback on an FM stereo receiver or radio. Of those products known, the Z-Wave FM transmitter and Sound feeder FM transmitter can be tuned to the entire FM band using a single dial-controlled variable capacitor or in conjunction with a band selector switch. These products use a simple Lxe2x88x92C oscillator for generating a carrier signal and are therefore prone to temperature drift, pulling due to magnetic fields, or simply bad phase noise. Another product, the Link-it transmitter, includes a channel switch for choosing between one of five channels. These products utilize standard and inferior off-the-shelf stereo encoders.
It is also known that a portable CD player distributed by Brookstone, Inc. includes an integrated FM transmitter tunable to any FM frequency by a dial-controlled variable capacitor.
Except for the Link-it product, the above products do not indicate the channel on which they are transmitting, and therefore the FM receiver must be tuned to locate the channel. This presents difficulties in use of the products, because a user will manually need to adjust the FM receiver to adapt to the signal being transmitted by the product transmitter. Also, since the selector of the channel is subject to being bumped or moved and the transmitter is subject to drifting, the transmitting channel may not be identical from one moment to another and may thus require readjusting the receiver. Further, inasmuch as the FM transmitter""s power output is purposely maintained low to prevent interference with other nearby radio listeners and regulatory restrictions, it is possible to tune the transmitter to a channel that is on or very close to a strong local channel, thereby masking the FM transmitter""s signal and preventing it from being found on the receiver.
It has also been known to provide an FM transmitter for converting an audio signal into an FM signal for transmission, that includes a circuit for detecting an unused FM frequency to set the transmitter to the detected unused frequency and display that frequency as disclosed in U.S. Pat. No. 5,970,390.
The problems heretofore found in wireless players are addressed by the wireless output input device (WOID) player of the present invention, particularly by providing a frequency synthesized FM transmitter and FM receiver integral with the player. By using a frequency synthesizer, the player can be completely microprocessor controlled. It should be appreciated that while the present disclosure is directed toward FM frequency, any other suitable frequency and modulation schemes could also be supported.
The FM transmitter of the WOID player of the present invention may be limited to producing signals on a discrete number of channels or it may have the ability to tune any channel within the FM band.
Once the FM transmitter functionality of the WOID player of the present invention is turned on, the transmitter automatically scans the FM band for the presence of other strong signals and determines the channel with the least amount of interference and automatically tunes the FM transmitter of the player to that channel. A display then indicates the frequency of the channel on which the player will be transmitting so that the FM receiver intended to receive the digital signal output of the player can be tuned to that channel.
When searching for a channel, if the FM transmitter of the WOID player of the invention is restricted to a number of discrete channels such as 15 channels distributed across the band, only those 15 channels will be searched to determine which channel has the least amount of interference. However, it will be appreciated that if the FM transmitter of the player is not limited to a discrete number of channels, a profile of the entire band will be generated by the player for searching.
Since the WOID player of the invention is particularly suited to be used in an automobile, it will be appreciated that a chosen FM channel may suffer from interference such as when going from one geographic area to another. While the user may manually request another channel, the player of the invention may be programmed to periodically monitor the interference level on the current channel and other channels by monitoring and estimating the signal to noise ratio (SNR) of the received audio. This ratio is explained herein to constitute the peak signal value to energy value ratio as a method used to estimate SNR. Should the SNR commence degrading, the search process for a channel of least interference may be automatically started, and when found, the player can cue the user to change the channel on the mobile or stationary FM receiver. Alternatively, the player may be programmed to continuously monitor the other possible transmission channels to see if another channel would be better than the current channel. Another alternative is to provide a built-in microphone of the player to monitor the audio output of the receiver for the presence of static or other interference present in the transmission, and if found, to then seek a better channel. Further, the device can overcome a degraded stereo FM broadcast by converting the signal from a stereo FM broadcast to an monaural FM broadcast. The device will do this because monaural FM broadcasting offers better SNR than stereo FM broadcasting. When the microphone and/or receiver detects that the stereo signal has degraded and a mono FM signal would provide a better signal to noise ratio, the player would automatically convert to monaural broadcasting without user intervention and prior to being switched automatically by the receiving radio.
Where a better station is found for transmission, the WOID player would send an audio and/or visual cue notifying the user to change channels to that indicated either in the display or audibly announced by a voice synthesizer or the like. The player would then listen via the microphone for the absence of a signal tone from the FM receiver to determine when the user had taken the recommendation to change the frequency of the FM receiver. Once the player has determined that the user has changed the receiver channel, the FM transmitter on the player would then automatically switch to the indicated channel. Accordingly, the player would allow the user to receive clear audio even when driving through long congested areas or over long distances while merely requiring the user to switch receiver channels in response to an audible tone or a visual cue. It would never be necessary to manipulate the device in this process.
It is therefore an object of the present invention to provide a WOID player for transmitting a digitally encoded stream of audio from a digital audio player to an FM receiver that produces high fidelity.
Another object of this invention is in the provision of a WOID player including an FM transmitter and an FM tuner which shares the digital processing power of the device""s CPU to perform digital stereo encoding, thereby maintaining the cost of the player at a low level because of the ability to use components already existing on the player.
A further object of the present invention is to provide a WOID player for transmitting digitally stored audio and which also includes an FM receiver that is used in conjunction with an auto scanning feature to determine an FM channel having the least amount of interference.
Another object of the present invention is to provide a WOID player having an all-digital stereo encoder, thereby making it possible to implement other forms of digital communications over the FM band.
Yet another object of the present invention is to provide a WOID player having a stereo encoder that accepts audio inputs from an outside source, and is capable of retransmitting that audio.
A further object of the invention is to provide a WOID player which implements other forms of digital communications over the FM band which will allow the creation of an inexpensive means to remotely (wirelessly) control or operate the player.
Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts.